Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A system and method for identifying a pulsed radiation source may include
an imaging sensor having a frame rate that is less than a pulse
repetition frequency (PRF) of the pulsed radiation source. A processing
unit may be in communication with the imaging sensor, and be configured
to (i) process a sequence of image data of a scene captured by the
imaging sensor to determine whether radiation of the pulsed radiation
source is detected, (ii) determine a PRF code of the pulsed radiation
source from possible multiple different PRF codes based on the processed
sequence of image data, and (iii) notify a user of the PRF code or
information associated with the PRF code.

Claims:

1. A system for identifying a pulsed radiation source, said system
comprising: an imaging sensor having a frame rate that is less than a
pulse repetition frequency (PRF) of the pulsed radiation source; and a
processing unit in communication with said imaging sensor, and configured
to: process a sequence of image data of a scene captured by said imaging
sensor to determine whether radiation of the pulsed radiation source is
detected; determine a PRF code of the pulsed radiation source from
possible multiple different PRF codes based on the processed sequence of
image data; and notify a user of the PRF code or information associated
with the PRF code.

2. The system according to claim 1, wherein said processing unit is
further configured to cause said imaging sensor to operate at the frame
rate and use an integration window, and process the sequence of image
data over a number of image frames for a data acquisition time.

3. The system according to claim 2, wherein said processing unit is
further configured to determine whether radiation of the pulsed radiation
source is detected or not detected in each of the frames during the data
acquisition time.

4. The system according to claim 3, wherein said processing unit is
further configured to determine a set of unique features based on
determining whether the radiation of the pulsed radiation source is
detected or not detected in the image frames captured by said imaging
sensor.

5. The system according to claim 1, wherein said processing unit is
further configured to determine geographic coordinates of an object from
which the radiation of the pulsed radiation source is being captured by
said imaging sensor.

6. The system according to claim 5, wherein said processing unit is
further configured to detect radiation from a second pulsed radiation
source while determining the PRF code of the pulsed radiation source.

7. The system according to claim 6, wherein said processing unit is
further configured to establish geographic coordinates of the second
pulsed radiation source.

8. The system according to claim 1, wherein said imaging sensor is
configured with a field-of-view greater than approximately five degrees.

9. The system according to claim 1, further comprising a user interface
that is configured to enable a user to set frame rate, and integration
window for a number of frames over a minimized wait time to process the
sequence of image data.

10. The system according to claim 1, wherein said processing unit, in
notifying the user of information associated with the PRF code, is
further configured to display an identification of a weapons system from
which the pulsed radiation source having the PRF code.

11. A method for identifying a pulsed radiation source, said method
comprising: processing a sequence of image data of a scene to determine
whether radiation of the pulsed radiation source is detected; determining
a pulsed repetition frequency (PRF) code of the pulsed radiation source
from multiple possible different PRF codes based on the processed
sequence of image data; and presenting the determined PRF code or
information associated with the PRF code to a user.

12. The method according to claim 11, further comprising using a frame
rate and integration window for capturing the image data, and processing
the sequence of image data over a number of image frames for a data
acquisition time.

13. The method according to claim 12, further comprising determining
whether radiation of the pulsed radiation source is detected or not
detected in each of the frames during the data acquisition time.

14. The method according to claim 13, further comprising determining a
set of unique features based on determining whether radiation of the
pulsed radiation source is detected or not detected in the captured image
frames.

15. The method according to claim 11, further comprising determining
geographic coordinates of an object from which the radiation of the
pulsed radiation source is being captured by said imaging sensor.

16. The method according to claim 15, further comprising detecting
radiation from a second pulsed radiation source while determining the PRF
code of the pulsed radiation source.

17. The method according to claim 16, further comprising establishing
geographic coordinates of the second pulsed radiation source.

18. The method according to claim 11, further comprising capturing the
image data using a field-of-view that is greater than approximately five
degrees.

19. The method according to claim 11, further comprising providing a user
interface configured to enable a user to set frame rate and integration
window for a number of frames over a minimized wait time to process the
sequence of image data.

20. The method according to claim 11, further comprising displaying an
identification of a weapons system from which the pulsed radiation source
having the PRF code in notifying the user of information associated with
the PRF code.

21. A method for configuring a system for detecting a pulsed radiation
source with optimized frame rates and wait times, said method comprising:
generating a simulated pulsed radiation source signal having a pulse
repetition rate τ and pulse width α; generating a simulated
camera integration signal having a frame rate σ and an integration
window β with phase offset δ; simulating a pulsed radiation
source search by determining if the pulse width α of the simulated
pulsed radiation source signal is completely within the integration
window β for the simulated camera integration signal over a
plurality of phase offsets δ of the integration window β;
creating a matrix for recording wait times determined for a range of
frame rates σ.sub.1-.sigma.m and range of pulse repetition
rates τ.sub.1-.tau.n of a pulsed radiation source being
simulated; in response to determining that the pulse width α of the
simulated radiation source is completely within the integration window
β of the simulated camera integration signal, entering a current
wait time into the matrix in association with the current frame rate
σ and pulse repetition rate τ; stepping the frame rate σ;
determining whether the frame rate σ is less than or equal to
σm, and if so, repeat generating, generating, simulating,
determining and entering; otherwise, stepping the pulse repetition rate
τ; determining whether the pulse repetition rate τ is less than
or equal to τn, and if so, repeat generating, generating,
simulating, determining and entering; otherwise, identifying a smallest
wait time in each column in the matrix for each of the pulse repetition
rates τ.sub.1-.tau.n; identifying optimal frame rates
σopt for each of the pulse repetition rates
τ.sub.1-.tau.n corresponding to the identified smallest wait
times; and configuring a system for identifying a pulsed radiation source
with the optimal frame rates σopt and corresponding identified
smallest wait times.

22. The method according to claim 21, wherein identifying optimal frame
rates σopt includes identifying from frame rates
σ.sub.1-.sigma.m that identify respective rows of the matrix
in which the identified smallest wait times are positioned.

23. The method according to claim 21, wherein the phase offsets δ
are approximately equivalent the integration window β.

Description:

BACKGROUND

[0001] As military systems developers have increasingly improved precision
of weapons and surveillance systems, the use of pulsed energy or
radiation sources has been a key component in achieving improved
precision. Generally speaking, pulsed radiation sources include lasers
that operate with a given pulse rate and pulse width. Different pulsed
radiation sources use different pulse rates and pulse widths.

[0002] Military personnel, whether acting offensively or defensively,
utilize sensing equipment to assist with offensive and defensive military
operations. From an offensive perspective, one operation for which
military personnel use sensing equipment is to monitor targets that are
being targeted by remote pulsed radiation sources to ensure the correct
target is being illuminated. Targets are generally illuminated by pulsed
radiation sources either by the weapons system itself or personnel on the
ground for the weapons system to target. From a defensive perspective,
one operation for which military personnel use sensing equipment is to
detect pulsed radiation sources from potential enemy weapons, thereby
providing military personnel to take preemptive action.

[0003] With regard to FIG. 1, a military field environment 100 shows field
personnel 102 using a camera 104 for viewing a scene 106 in which
military equipment 108a and 108b (collectively 108) being targeted by a
helicopter 110 using a pulsed radiation source, such as a laser, to track
and provide guidance for a weapons system. Typical pulsed radiation
sources have a very short duty cycle relative to their pulse rate. For
example, a laser or LED with less than one microsecond (μs) pulse
width and pulse repetition frequency of 15 Hz may be typical of a pulsed
radiation source.

[0004] Historically, cameras used to detect pulsed radiation sources have
used a single sensor that is separate from the imaging sensor system. The
single sensors are generally avalanche photo diodes (AVP) or pin diodes,
which are analog sensors. The inclusion of a separate sensor from an
imaging sensor results in increased camera weight and power consumption,
both of which are valuable commodities for field personnel. The single
sensor typically has a very narrow field-of-view, generally less than 1-
degree, and is limited to detecting one laser at a time. In addition, the
single sensor that needs to be boresighted or otherwise calibrated to the
imaging system of the camera. Using a camera with the single sensor to
detect pulsed radiation sources results in these problems and other
operational limitations for field and other military personnel.

SUMMARY

[0005] To detect and determine characteristics of pulsed radiation
sources, a system that uses an imaging sensor for sensing pulsed
radiation sources and processes image data captured by the imaging sensor
is provided. By using the imaging sensor rather than a single, separate
sensor from the imaging sensor to detect a pulsed radiation source, the
system has increased field-of-view, weighs less, consumes less energy,
and is capable of tracking multiple pulsed radiation sources
simultaneously.

[0006] One embodiment of a system for identifying a pulsed radiation
source may include an imaging sensor and processing unit in communication
with the imaging sensor. The processing unit may be configured to (i)
process a sequence of image data of a scene captured by the imaging
sensor to determine whether radiation of the pulsed radiation source is
detected, (ii) determine a PRF code of the pulsed radiation source from
possible multiple different PRF codes based on the processed sequence of
image data, and (iii) notify a user of the PRF code or information
associated with the PRF code.

[0007] One method for identifying a pulsed radiation source may include
processing a sequence of image data of a scene to determine whether
radiation of the pulsed radiation source is detected. A pulsed repetition
frequency (PRF) code of the pulsed radiation source may be determined
from among multiple possible different PRF codes based on the processed
sequence of image data. The determined PRF code or information associated
with the PRF code may be presented to a user.

[0008] One method for configuring a system for detecting a pulsed
radiation source with optimized frame rates and wait times may include
generating a simulated pulsed radiation source signal having a pulse
repetition rate τ and pulse width α. A simulated camera
integration signal having a frame rate σ and an integration window
β with phase offset δ may be generated. A pulsed radiation
source search may be simulated by determining if the pulse width α
of the simulated pulsed radiation source signal is completely within the
integration window β for the simulated camera integration signal
over a plurality of phase offsets δ of the integration window
β. A matrix may be created for recording wait times determined for a
range of frame rates σ1-σm and range of pulse
repetition rates τ1-τn of a pulsed radiation source
being simulated. In response to determining that the pulse width α
of the simulated radiation source is completely within the integration
window β of the simulated camera integration signal, a current wait
time may be entered into the matrix in association with the current frame
rate σ and pulse repetition rate τ. The frame rate σ may
be stepped. A determination as to whether the frame rate σ is less
than or equal to σm, and if so, repeat the generating,
generating, simulating, and determining and entering steps. Otherwise,
the pulse repetition rate τ may be stepped. A determination as to
whether the pulse repetition rate τ is less than or equal to
τn, and if so, repeat the generating, generating, simulating,
and determining and entering steps. Otherwise, a smallest wait time in
each column in the matrix may be identified for each of the pulse
repetition rates τ1-τn. Optimal frame rates
σopt may be identified for each of the pulse repetition rates
τ1-τn corresponding to the identified smallest wait
times. A system for identifying a pulsed radiation source with the
optimal frame rates σopt and corresponding identified smallest
wait times may be configured.

BRIEF DESCRIPTION

[0009] Illustrative embodiments of the present invention are described in
detail below with reference to the attached drawing figures, which are
incorporated by reference herein and wherein:

[0010] FIG. 1 is an illustration of an illustrative military field
environment in which field personnel use a camera system to sense pulsed
radiation sources;

[0011]FIG. 2 is a block diagram of electronic components of an
illustrative camera system that uses an imaging sensor for sensing a
scene and generating image data for use in tracking pulsed radiation
sources and determining pulse repetition frequency codes of the pulsed
radiation sources;

[0012]FIG. 3 is a flow diagram of an illustrative process for processing
image data to determine a pulse repetition rate of a pulsed radiation
source;

[0013]FIG. 4 is a graph of illustrative signals that are used to
illustrate sensing parameter definitions that may be used by a tracking
system to detect radiation produced by a pulsed radiation source in
accordance with the principles of the present invention;

[0014] FIGS. 5A and 5B are graphs of illustrative best and worst wait
times for a sensing system (e.g., FIG. 2) to determine whether a tracking
system has correctly matched frequency and phase of a pulsed radiation
source;

[0016]FIG. 7A is a flow diagram of an illustrative process for simulating
and calculating wait times for a tracking system to conclusively
determine pulse repetition rate of a pulsed radiation source;

[0017]FIG. 7B is a flow diagram of an illustrative process for
configuring a system for detecting a pulsed radiation source with
optimized frame rates and wait times;

[0018] FIGS. 8A and 8B are illustrative IR integration windows and pulsed
radiation sources used for illustrating when a pulsed radiation source is
detected in an IR integration window;

[0019]FIG. 9 is an illustration of an illustrative maximum wait time
table used for collecting maximum wait times determined by the simulation
process of FIG. 7A;

[0020]FIG. 10 is an illustration of how the maximum wait time table of
FIG. 9 may be used to find the optimal IR frame rate to use when
searching for each PRR of the pulsed radiation source (e.g., laser);

[0021]FIG. 11 is a graph of illustrative optimal frame rates for each
pulse repetition rate of pulsed radiation sources produced by the
simulation of FIG. 7A;

[0022]FIG. 12 is a graph of illustrative wait times for each pulse
repetition rate of pulsed radiation sources produced by the simulation of
FIG. 7A;

[0023]FIG. 13 is a flow diagram of an illustrative process for detecting
and processing image data to determine a pulse repetition frequency code
of a pulsed radiation source by a field operated weapons or surveillance
system;

[0024]FIG. 14 is a flow diagram of an illustrative process for
determining pulse repetition frequency code of a pulsed radiation source
by a field operated weapons or surveillance system;

[0025] FIG. 15 is a graph of an illustrative IR frame window signal for
use in detecting a pulse repetition rate signal of a pulsed radiation
source using the smallest or optimal wait times for each of the optimal
IR frame rates;

[0026]FIG. 16 is a timing diagram of an illustrative process for
detecting, tracking, and identifying multiple pulsed radiation sources
within a field-of-view of the camera;

[0027] FIGS. 17A and 17B are illustrations of illustrative targets that
are being tracked by an imaging sensor within the field-of-view of a
camera; and

[0028] FIGS. 18A and 18B are screen shots of illustrative images of a
scene when tracking a single and multiple radiation sources,
respectively.

DETAILED DESCRIPTION

[0029] With regard to FIG. 2, a block diagram of electronic components of
an illustrative camera 200 is shown. The camera 200 may be configured to
record imaging data of a scene in one or more bands of optical or
non-optical frequencies. The term "camera" may be used to describe an
electro-optical system that collects or does not collect image data, such
as binoculars, telescopes, or any other system that is configured to
identify characteristics of pulsed radiation sources. The characteristics
of the pulsed radiation sources may include pulse repetition frequency
codes of pulsed radiation sources to identify a type of pulsed radiation
source that is illuminating a target or other object. The camera 200 may
include dual-band optics 202 that are configured to receive an optical
signal 204, such as that in the 1.06 micrometer range, and midwave
infrared frequency (MWIF) signal 206. In one embodiment, the dual
band-optics 202 are configured to provide a field-of-view that is greater
than approximately five degrees. It should be understood that the
dual-band optics 202 may include multi-band optics configured to operate
over more than two frequency bands.

[0030] The dual-band optics 202 are configured to illuminate a focal point
array (FPA) or imaging sensor 208 with photons 210 representative of a
scene being within the field-of-view of the dual-band optics 202. The
imaging sensor 208 has a certain number of pixels along azimuth and
elevation planes, as understood in the art. In one embodiment, the
imaging sensor 208 is configured with 640 pixels along an azimuth
direction and 480 pixels along an elevation direction (i.e.,
640×480). The imaging sensor 208 may be enclosed within a dewar 212
to maintain the imaging sensor 208 at a temperature at which the imaging
sensor 208 is more sensitive to the photons 210 being imaged onto the
imaging sensor 208. To control the temperature of the dewar 212, a
cryo-engine 214 may be in communication with the dewar 212 to control the
temperature of the dewar 212, as understood in the art. A cooler drive
216 may be configured to receive a temperature sense signal 218, which is
a feedback signal, and generate a temperature drive signal 220 for the
cryo-engine 214. The cryo-engine 214, in turn, drives the temperature of
the dewar 212 to regulate temperature of the imaging sensor 208. In an
alternative embodiment, the imaging sensor may be an uncooled image
sensor.

[0031] The camera 200 may further include a processing unit 222 that
executes software 224. The processing unit 222 may execute the software
224 to control the imaging sensor frame rate and integration time and to
collect and process imaging sensor data 226 that is being collected from
the imaging sensor 208. The processing unit 224 may be configured to
process the sensor data 226 to detect, identify, and track a pulsed
radiation source generating an illumination signal (e.g., laser beam)
within the field-of-view of the dual-band optics 202 that are being
imaged onto the imaging sensor 208. The software 224 may further be
configured to determine characteristics of the pulsed radiation sources,
such as a pulse repetition frequency (PRF) or pulse repetition rate
(PRR), which, as understood in the art, are inverses of one another,
codes of the pulsed radiation source being tracked, and present the PRR
or PRF to a user. Based on the PRF or PRR, a PRF code number identifying
the pulsed radiation source being used to generate the illumination
source may be determined and presented to the user.

[0032] As understood in the art, the imaging sensor 208 may have a variety
of sensor parameters that are used to control functional operation of the
imaging sensor 208. The sensor parameters may include (i) frame rate and
(ii) integration time that creates an "electronic shutter" (i.e., the
length of time that the imaging sensor 208 is allowed to sense external
image signals over one or more frequency bands). In addition, the imaging
sensor 208 may be configured to operate in a "snap-shot" mode, where
every pixel detector in the imaging sensor turns on and turns off at the
same time. A user of the camera 200 may interact with a user interface
228 to set sensor parameters 230 for configuring the imaging sensor 208.
The user interface 228 may include knobs, buttons, touch screen display,
remote control, or any other mechanical and/or electrical user interface
that allows for selecting one or more sensor parameters to configure
operation of the imaging sensor 208. In addition, the user interface 228
may include an electronic display (see FIGS. 18A and 18B) that is capable
of displaying image data and PRF code(s) that are detected in the image
data.

[0033] In one embodiment, the image data may include an actual image of a
scene of which the dual-band optics 202 are capturing. In addition, the
image data being displayed on the user interface 228 may include pulsed
radiation source information showing coordinates (e.g., azimuth,
elevation, range) on the imaging sensor 208 and/or of a location within
the scene at which radiation (e.g., optical signal) is being reflected
from an object (e.g., building) or from the pulsed radiation source
directly. The coordinates within the scene may be geographic coordinates,
which include relative coordinates in any coordinate format (e.g.,
Cartesian) from the camera itself. More specifically, the geographic
coordinates define a location at which the pulsed radiation source is
illuminating (e.g., on the side of a building) or at the pulsed radiation
source itself (e.g., at the weapons system). Still yet, the user
interface 228 may be configured to display both image data and
representative pulsed radiation source data (e.g., icon or other indicia)
to better indicate to a user a specific target or object that the pulsed
radiation source is illuminating. If more than one pulsed radiation
source is being tracked, then the user interface 228, in response to
receiving more than one pulsed radiation source code, may display the
pulsed radiation source codes in a list or in association with an
indicator on the user interface 228.

[0034] With regard to FIG. 3, a flowchart of an illustrative process 300
for processing image data and determining pulse repetition rate of a
pulsed radiation source is shown. The process 300 starts at step 302,
where a sequence of image data captured from an imaging sensor is
processed. The sequence of image data may include multiple, sequential
frames that are being collected by the imaging sensor of a scene within
the field-of-view of the imaging sensor. The frames of image data may be
captured at a certain frame rate and integration window, as configured by
sensor parameters that are set by a user or manufacturer. At step 304, a
pulse repetition rate or frequency of a pulsed radiation source may be
determined based on a processed sequence of image data. The pulse
repetition rate or frequency may be displayed to a user to determine a
particular type of pulsed radiation source that is being used to target
or otherwise illuminate a structure or object. In one embodiment, a
pulsed radiation rate, sometimes called pulsed repetition frequency code
or simply PRF code, that identifies the pulsed radiation source
generating a pulsed radiation signal may be determined based on the
determined pulse repetition rate. In another embodiment, rather than
displaying the pulse repetition rate, the pulse repetition frequency code
or other characteristic or identifier of the pulsed radiation source may
be displayed.

[0035]FIG. 4 is a graph 400 of illustrative sensor signals and pulsed
radiation source signals that are used to illustrate variable definitions
that define both the pulse radiation source signals and sensor signals.
The graph 400 includes a series of integration windows 402a-402n
(collectively 402) that are arranged in integration window sets 404a,
404b, and 404c generated by an imaging sensor. Although shown as
different amplitudes, the integration windows 402 of the integration
window sets 404a, 404b, and 404c may each have the same amplitudes. Also
shown on the graph 400 are a series of pulsed radiation source signals
406a-406n (collectively 406) produced by a pulsed radiation source, such
as a laser. The series of integration windows 402, although shown as five
integration windows in each of the integration window sets 404a, 404b,
and 404c, may have a different number of integration windows for each set
depending upon a minimum wait time determined to provide for unambiguous
verification of a frequency of the pulsed radiation source signals 406.
For example, rather than having five integration windows for each of the
integration window sets 404a, 404b, and 404c, the number of integration
windows may be eight, for example, depending upon what variables or
parameters are being used by both a tracker system and pulsed radiation
source, as further described herein with regard to FIG. 7A.

[0036] Continuing with FIG. 4, a number of different variables or
parameters are used to define the pulsed radiation source signals 406.
The parameters include (i) frame rate σ, (ii) integration time
β, (iii) imaging sensor phase delay φ1, (iv) master
reference φ, (v) pulsed radiation source phase delay φ2. A
frame rate σ is the time or frequency between the start of
integration windows. Integration time β defines a time of each of
the integration windows. An imaging sensor phase delay φ1, which
in this case is zero since the first integration window 402a is aligned
with t0 defines a start delay from time t0. A pulsed radiation
source phase delay φ2, which in this case is 0.0174 seconds,
defines a start delay from time t0. A master reference φ may be
used as a master clock and set at a base value, such as 0.1 ms. Each of
the integration window sets 404 operate for enough time to detect a pulse
of the pulsed radiation source if the tracker system is in phase with the
pulsed radiation source. In the event that the tracker system does not
detect a pulse of the pulsed radiation source within an integration
window set, then a phase offset, which is a time delay in starting a next
integration window set (e.g., integration window set 404b) from the
previous integration window set (e.g., integration window set 404a), may
be applied. By phase shifting the integration window sets, a
determination may be made as to whether phase or frequency is to be
adjusted to determine a pulse repetition rate or frequency of the pulsed
radiation source.

[0037] With regard to FIGS. 5A and 5B, respective charts 500a and 500b
showing histograms of best (i.e., shortest) times and worst (i.e.
longest) times for being able to conclusively determine a pulse
repetition rate of a pulsed radiation source are shown. As shown in FIG.
5A, times for conclusively determining pulse repetition rate of a pulse
radiation source range from approximately 0.1 seconds to approximately
0.4 seconds, while times shown in FIG. 5B range from approximately 10
seconds to nearly 150 seconds. The difference between the best times of
FIG. 5A and worst times of FIG. 5B is the result of predetermining
optimal frame rates of the imaging sensor for pulse repetition rates of
pulsed radiation sources in accordance with the principles of the present
invention. In determining optimal frame rates, a software simulation (see
FIG. 7A) may be run for each pulse repetition rate of the pulsed
radiation sources to determine which frame rates were able to acquire or
conclusively determine the pulse repetition rate the fastest and the
amount of time it took for conclusively making the determination (i.e.,
minimum wait time).

[0038] With regard to FIG. 6A, a graph 600a of an illustrative IR
integration window signal 602 showing two IR integration windows 604a and
604b. Each of the integration windows 604a and 604b have a pulse width of
β and operate at a frame rate of σ. The pulse width β and
frame rate σ are used in determining minimum wait times, as
calculated by the process of FIG. 7A.

[0039] With regard to FIG. 6B, a graph 600b of an illustrative pulsed
radiation source signal 606 showing two pulsed radiation source signal
pulses 608a and 608b. Each of the pulsed radiation signal pulses 608a and
608b have a pulse width of α and operate at a pulse repetition rate
of τ. The pulse width χ and pulse repetition rate τ are used
in determining minimum wait times, as calculated in the process of FIG.
7A. As shown, both the IR integration window signal 602 and pulsed
radiation source signal 606 are synchronized in that the IR integration
window 604a and pulsed radiation source pulse 608a each start at time
t0. It should be understood, however, that it is rare that a tracker
system is initially synchronized with the pulsed radiation source.
Typically, the IR integration window 604a is offset from the pulsed
radiation source signal pulse 608a.

[0040] With regard to FIG. 6c, the IR integration window signal 602 is
shown to have a delay of δ, which causes the first integration
window 604a to not be aligned with the pulsed radiation source pulse 608a
of FIG. 6B. The delay δ is varied in the process of FIG. 7A in an
attempt to identify a pulse of the pulsed radiation source (FIG. 6B).

[0041] With further regard to FIG. 6c, it should be understood the α
is typically very short with respect to β. And since the separation
in time of neighboring τ-repetition rates (typically separated by
0.001 seconds) allows for more than one τ-valued signal to appear
within the β-window, the continued detection of the pulse at every
expected opportunity is observed over a period of time in order to
confirm the correct τ has been detected. If the pulse source of
τ-value differs from the expected value, then the pulse, over time,
will appear to walk out of the β-window. The length of time for the
pulse to exit the β-window and the direction in which it exits
(beginning of β-window or end of β-window) is a function of
β, σ, and τ. TABLE I shows the additional confirmation
wait-times used to separate a τ±0.001 seconds from the expect
τ. TABLE I further shows wait-time (seconds) for various laser code
samples used to confirm that the τ is correct and not±one code
offset.

[0042] With regard to FIG. 7A, a flow chart of an illustrative process 700
for simulating and calculating wait times for a tracking system to
conclusively determine pulse repetition rate of a pulsed radiation source
is shown. "Wait time" is used when searching for an IR frame rate that
enables the user to see the laser pulse. Wait time refers to the amount
of time the video stream is monitored for a pulsed radiation source after
setting the IR frame rate (σ) and the IR frame rate phase shift
(δ) to new values. It should be understood that the wait time may
be defined by numbers of frames or other video parameter as opposed to
units of time (e.g., seconds). The process 700 starts at step 702, where
a loop of all values of interest of τ and all values of interest of
σ starts. At step 704, a process is started to find the smallest
integers of J and K such that Kσ=Jτ. As an example, if
τ=100 and σ=25, using basic algebra, τ/σ=100/25=4,
which provides for the smallest integers for J and K to be K/J=4/1=4.

[0043] At step 706, a loop starts for all values of interest of δ
(i.e., delay). It should be understood that δ increments may be
based on clock rate, camera resolution, and/or other physical parameters
of the tracking system. At step 708, a third loop starts for all j's and
k's, such that j ranges from 0 to J and k ranges from 0 to K, where j and
k are integers. At step 710, a determination may be made as to whether
kσ+δ≧jτ-(β-α) and whether
kσ+δ≦jτ. If so, then it is determined that a
pulsed radiation source signal is found during an integration window, as
demonstrated in FIGS. 8A and 8B. If a pulsed radiation source signal is
found at any step of k, then that step value of k is saved.

[0044] With regard to FIG. 8A, illustrative integration window and pulsed
radiation source signals 800a are shown to demonstrate the equation of
kσ+δ=jτ-(β-χ), which determines whether a pulsed
radiation source signal pulse 802 is within a right-most edge 803 of an
integration window 804. The start time of the pulsed radiation source
signal pulse 802 is determined by jτ and integration window 804 is
determined by kσ+δ.

[0045] With regard to FIG. 8B, illustrative integration window and pulsed
radiation source signals 800b are shown to demonstrate the equation
kσ+δ=jτ, which determines whether a pulsed radiation
source signal pulse 806 is within a left-most edge 805 of the integration
window 804. As with FIG. 8A, the start time of the pulsed radiation
source signal pulse 806 is determined by jτ and integration window
808 is determined by kσ+δ.

[0046] Continuing with FIG. 7A, at step 712, if j<J or k<K, then the
process 700 loops back to step 708 and the loop continues to repeat until
both j=J and k=K. If j=J and k=K, then the process 700 continues at step
714, which determines whether all values of interest of δ (i.e.,
time delay) have been tested. If not, then the process 700 loops back to
step 706 to step δ to a next value and repeats the inner loop. Once
all values of interest of δ have been processed, the process
continues to step 716. At step 716, a determination of the maximum wait
time for the current τ and σ combination is made. The largest
wait time is determined as the largest gap between k's that are saved. As
an example, if within a j loop, where j=1, if it is determined at k=1, 3
and 4 that a pulsed radiation source signal pulse is within an
integration window, then k=1, 3, and 4 are saved. The largest gap between
the saved k's is 2 (i.e., (k=3)-(k=1)=2), which is multiplied by σ
and stored in the corresponding cell for σ and τ (e.g., upper
left cell corresponding to cell σ1 and τ1 (see FIG. 9)). At
step 718, if additional value of τ and σ exist, then the
process returns to step 702 to repeat for all values of interest of τ
and σ.

[0047] With regard to FIG. 11, an illustrative graph 1100 provides optimal
frame rates for each given pulse repetition rate or frequency of pulsed
radiation sources. The United States uses a certain number of pulse
repetition frequencies for various pulsed radiation sources, and each one
of those frequencies ranges over certain frequencies. In identifying and
synchronizing with the different pulsed radiation sources by a tracking
system, optimal frame rates as determined by the simulation provided in
FIG. 7A may be utilized.

[0048] Two scenarios exist when using a tracking system for detecting
pulsed radiation sources, (i) knowing what PRF is being used by the
pulsed radiation source, and (ii) not knowing what PRF is being used by
the pulsed radiation source. No matter which one of the two scenarios
exists in the field, the optimal frame rate may be used to most quickly
detect, identify, and track the pulsed radiation source. As an example,
with a pulsed radiation source having a PRF of PRF1 Hz, a
corresponding optimal frame rate is defined by point 1102, which is F+20
Hz. It should be understood that each laser PRF shown on the chart 1100
has a single optimal frame rate associated therewith. The optimal frame
rates are data points generated by the process 700 of FIG. 7A and stored
in tables, such as those shown in FIGS. 9 and 10. As another example, in
the case in which the frequency of the pulsed radiation source is
unknown, the imaging system may select a frame rate in which multiple
pulsed radiation source PRFs may be detected using the same frame rate of
the imaging sensor. Alternatively, the system may start at a lowest PRF
and step its way up the certain number of different PRFs until the
correct frame rate is determined. As shown, the lowest PRF is
approximately PRF2 Hz, which corresponds to an optimal frame rate of
approximately F+4.4 Hz at point 1104.

[0049] With regard to FIG. 12 an illustrative graph 1200 showing
predetermined wait times for each corresponding pulsed radiation source
PRF is shown. Following with the examples of FIG. 11 with a pulsed
radiation source PRF of PRF1 Hz, a wait time is predetermined to be
set at T+0.16 seconds at point 1202. In addition, a pulsed radiation
source PRF of PRF2 Hz is shown to be associated with a wait time of
approximately T+0.065 seconds at point 1204. It should be understood that
the wait time associated with each pulsed radiation source PRF is
computed based on the simulation of FIG. 7A performed to determine how
long it takes for each pulsed radiation source PRF to be determined
without ambiguity. The wait times are identified in the table of FIG. 10.
The wait time provides an amount of time that the system waits before
doing a phase shift in an attempt to sense a pulse of the pulsed
radiation source during an integration window of the tracking system.
During this wait time, a number of integration windows are performed. To
determine the number of integration windows, the wait time is divided by
the integration window time. For example, a wait time of 16 milliseconds
is divided by an integration window of 6 milliseconds, which results in
2.67 integration windows, which is rounded up to an integer of 3
integration windows. In other words, each wait time is to have 3
integration windows before changing phase.

[0050] With regard to FIG. 9, an illustrative maximum wait time table 900
of maximum wait times is shown. The table 900 contains time values that
are defined by maximum k difference values multiplied by the σ
value being tested. The table 900 is filled in at step 716 (FIG. 7A) by
maximum wait time values, as described above. The table 900 is used to
find the IR frame rate (σ) that minimizes the wait time when
searching for each pulsed radiation source PRR (τ).

[0051] Continuing with FIG. 7A, at step 720, for each pulse repetition
rate τ, the smallest wait time is determined (i.e., smallest value in
each column). By finding the smallest wait times, the best of the worst
wait times in table 900 (FIG. 9) are identified. At step 722, the frame
rate σ at which the smallest wait time was determined at step 720
is determined to correspond to the optimal frame rate to use by the
tracking system when searching for a pulse of the pulsed radiation source
having a pulse repetition rate of τ. That is, the optimal frame rate
σ for each pulse repetition rate τ is the row with the smallest
table entry in the column of the current pulse repetition rate τ
(i.e., the optimal frame reate to use when searching for a given pulsed
radiation source PRR is that frame rate that yields the shortest wait
time). It should be understood that some optimal frame rates may
correspond to multiple pulse repetition rates τ.

[0052] With regard to FIG. 10, an illustrative maximum wait time table
1000 showing smallest wait times at each pulse repetition rate τ of
pulsed radiation sources and corresponding optimal frame rates δ of
a tracker system are shown be circled cells 1002a-1002n. Using the
smallest wait times and corresponding optimal frame rates by the tracking
system shortens the amount of time that the tracking system takes to
unambiguously identify and track a pulsed radiation source, whether or
not the pulse repetition rate is known, as illustrated by FIGS. 5A and
5B.

[0053] With regard to FIG. 7B, a flowchart of an illustrative process 730
for configuring a system for detecting a pulsed radiation source with
optimized frame rates and wait times is shown. The process 730 starts at
step 732, whereby a simulated pulsed radiation source signal having a
pulse repetition rate τ and pulse width α is generated. The
pulse repetition rate τ may be set to a first pulse repetition rate
τ1, as previously described in FIG. 7A, and the pulse width may
be set to a known pulse width of pulsed radiation sources. At step 734, a
simulated camera integration signal having a frame rate σ and an
integration window β with phase offset δ may be generated. The
frame rate σ may be set to a first frame rate α1, as
previously described in FIG. 7A, and the phase offset may be set to a an
integration window β. Alternative values for the phase offset
δ may be utilized in accordance with the principles of the present
invention.

[0054] At step 736, a pulsed radiation source search may be simulated by
determining if the pulse width α of the simulated pulsed radiation
source signal is completely within the integration window β for the
simulated camera integration signal over multiple phase offsets δ
of the integration window β. The multiple phase offsets δ
means that the integration window β is shifted in time by a phase
offset δ. At step 738, a matrix may be created for recording
longest wait times determined for a range of frame rates
σ1-σm and range of pulse repetition rates
τ1-τn of a pulsed radiation source being simulated. It
should be understood that data representations other than a matrix may be
utilized and considered equivalent to a matrix.

[0055] At step 740, in response to determining that the pulse width a of
the simulated radiation source is completely within the integration
window β of the simulated camera integration signal, a current wait
time may be entered into the matrix in association with the current frame
rate σ and pulse repetition rate τ. The frame rate σ may
be stepped at step 742. In stepping the frame rate σ, the frame
rate σ is stepped from σ1-σm in equal or
non-equal increments. At step 744, a determination as to whether the
frame rate σ is less than or equal to σm, and if so,
repeat generating (step 732), generating (step 734), simulating (step
736), and determining and entering (step 740). Otherwise, the pulse
repetition rate τ is stepped. In stepping the pulse repetition rate
τ, the pulse repetition rate τ is stepped from
τ1-τn in equal or non-equal increments. At step 748, a
determination is made as to whether the pulse repetition rate τ is
less than or equal to τn, and if so, repeat generating (step
732), generating (step 734), simulating (step 736), and determining and
entering (step 740). Otherwise, the process continues at step 750.

[0056] At step 750, a smallest wait time in each column in the matrix is
identified for each of the pulse repetition rates
τ1-τn. At step 752, optimal frame rates σopt
are identified for each of the pulse repetition rates
τ1-τn corresponding to the identified smallest wait
times. In one embodiment, identifying the optimal frame rates
σopt includes identifying from frame rates
σ1-σm that identify respective rows of the matrix
in which the identified smallest wait times are positioned. A system may
be configured for identifying a pulsed radiation source with the optimal
frame rates σopt and corresponding identified smallest wait
times. The system may be a camera system, weapons system, or any other
system that may be utilized to detect radiation of a pulsed radiation
source.

[0057] With regard to FIG. 13, a flowchart of an illustrative process 1300
for detecting and processing image data to determine a pulsed repetition
frequency code of a pulsed radiation source the optimal wait times as
determined by the process of FIG. 7A is shown. Because the sensor
parameters may not cause the imaging sensor to be in sync with pulses or
spots of a pulsed radiation source, it is possible that the imaging
sensor does not detect the pulsed radiation source at every "snap-shot"
of the imaging sensor. Using this principle, the process 1300 may start
at step 1302 by a determination being made as to whether or not a planned
laser or pulsed repetition rate code (τ) is being used. A planned
laser code is used if personnel projecting the pulsed radiation source
notifies personnel who are attempting to detect and track the pulsed
radiation source. If the laser code is not planned, then the process
continues at step 1304, where a first or next FLIR frame rate (σ),
integration time (β), maximum number of phase shifts, and number of
frames are selected. The selection process of step 1304 may be performed
manually, semi-automatically (e.g., select one or more settings to cause
predetermined other settings to occur), or automatically (e.g.,
preprogrammed next setting). The process continues at step 1306, where a
determination may be made as to whether to end the search for the pulsed
repetition rate code (τ). If it is determined at step 1306 that the
search for the pulsed repetition rate code (τ) is ended, then the
process is restarted and returns to step 1304. Otherwise, the process
1300 continues at step 1308, where the FLIR frame rate (σ),
integration time (β), number of phase shifts, and number of frames
are set. In one embodiment, the parameters (i.e., FLIR frame rate
(σ), integration time (β), number of phase shifts, and number
of frames) may be set by the results of the simulation process 700 of
FIG. 7A, thereby minimizing the wait time for an operator attempting to
detect, track, and identify the pulsed radiation source. In this case,
the number of frames is computed by dividing the wait time from FIG. 10
by the IR frame rate (σ) and rounding up. The wait time is found in
FIG. 10 at the intersection of the current IR frame rate (σ) with
the pulsed radiation source PRR currently being tested for the pulsed
repetition rate code (τ).

[0058] After the parameters are set at step 1308, image inputs, including
an initial image 1310a and next MWIR image(s) 1310b may be collected by a
camera being used by the operator to detect, track, and identify the
pulsed radiation source, as previously described. At step 1312, spots
detected may be localized in the image using x,y coordinates. It should
be understood that alternative coordinates may be utilized. If, at step
1314, a determination is made that a spot is detected, then the process
continues at step 1316, where the FLIR frame containing a pulsed
radiation source spot may be used as a first frame in a sequence of a
form feature vector in a process of FIG. 14. Otherwise, the process 1300
continues searching for pulsed radiation source spots using the current
set of parameters (see, for example, FIGS. 6A-6C) and continues taking
MWIR images 1310b until either (i) a spot is detected, in which case the
process 1300 continues through step 1316 to the process of FIG. 14 or
(ii) a determination is made at step 1318 that the number of frames has
ended, thereby signifying that the camera is not at the correct frequency
or phase to match the pulse repetition rate of the pulsed radiation
source.

[0059] If it is determined at step 1318 that the end of the number of
frames is reached, meaning the number of frames for a given FLIR frame
rate (σ) has reached its end without detecting a spot, then the
process 1300 continues at step 1322, where phase of the FLIR is shifted
by one integration time (β) (see FIG. 6c). After the FLIR is
shifted, another initial image 1310a is taken and the process 1300 cycles
again in an attempt to detect a spot so that the process of FIG. 14 can
commence. If the process 1300 does not detect a spot, then the process
1300 continues at step 1324, where a determination of whether a planned
laser code (τ) is set or not. If so, then the process continues at
step 1308. Otherwise, the process continues at step 1304 and the process
1300 repeats for a first set of parameters (step 1308) or next set of
parameters (step 1304).

[0060] With regard to FIG. 14, a flowchart of an illustrative process 1400
for determining a PRF code of a pulsed radiation source is provided. The
process 1400 is initiated in response to a spot being detected by the
process 1300 of FIG. 13, where the process 1400 is called by step 1316
with the detected spot of the pulsed radiation source is set in a first
frame in a sequence of a form feature vector.

[0061] Pulse repetition frequency codes generally range from approximately
8 Hz to slightly more than 19 Hz. Because imaging sensors, such as
imaging sensor 208 of FIG. 2, are not analog and do not generate
continuous, uninterrupted image data synchronization of the imaging
sensor with an unknown PRF code is generally not possible. As such, the
principles of the present invention provide for setting parameters for
the imaging sensor and using image data collected by the imaging sensor
of a scene in which a pulsed radiation source is being used may provide
enough information for the camera to accurately determine a particular
PRF code from among multiple PRF codes. As understood in the art, there
are currently 448 PRF codes from which a camera utilizing the principles
of the present invention identifies a PRF code being utilized by a pulsed
radiation source. However, the number of PRF codes may change over time,
but the principles of the present invention may operate as described
herein to accurately determine a particular PRF code from among an
increased or decreased number of PRF codes.

[0062] The process 1400 is used to process image data 1402 of a scene
collected by optics and imaging sensor of a camera once a spot of a
pulsed radiation source is detected by the process 1300 of FIG. 13, as
previously described. The imaging sensor generates sequential frames of
sensor data, which may be examined as pairs of sensor data 1402a and
1402b (collectively 1402) to generate differential image data for spot
detection as localized x,y coordinates. The process 1400, which may be
software executed by a processor on the camera system, may detect a
pulsed radiation source spot in the sensor data by subtracting the
successive sensor data frames 1402 at step 1404. For example, data frame
1402a may be subtracted from data frame 1402b to determine if an IR spot
is collected by the imaging sensor in either data frame 1402a or 1402b.
Step 1404 enables isolation of coordinates on the imaging sensor (i.e.,
x,y pixel(s)) that are illuminated by the spot. Detectors on the imaging
sensor may provide relative energy from each spot. Because of the
asynchronousness between the pulsed radiation source and frame rate of
the imaging sensor, the pulsed radiation source spot will not be present
in every image frame, which allows the camera to reduce false alarms from
other hot objects (i.e., IR sources near the pulsed radiation source
spot).

[0063] At step 1406, a determination may be made as to whether a spot of a
pulsed radiation source was detected in the successive sensor data frames
1402. If a spot is detected, then a spot detection parameter may be set
to logical `true` or `1.` Otherwise, if no spot is detected between
successive sensor data frames 1402, then the spot detection parameter may
be set to logical `false` or `0.` The spot detection parameter may be
included in a frame spot array or vector (or matrix) that accumulates
when spots are detected. At step 1408, a determination is made as to
whether a last image frame has been captured that meets the minimum wait
time or some other amount of time that is determined to enable tracking
and identification of a pulsed radiation source.

[0064] At step 1410, after completion of the image frames over a given
time period, the detection array of N-values (`1` for detection, `0` for
no detection) may be used to start a track file for the pulsed radiation
source detected in the sensor data for N-frames total, where N may be
greater than or equal to 300 and less than or equal to 500. Other numbers
of frames may be utilized in accordance with the principles of the
present invention. At step 1412, a detection array, which may be the same
or different from the frame spot array generated by looping through step
1406, of N-values for tracking multiple pulsed radiation sources is
generated. As with the frame spot array, the detection array may include
a "1" for detection and "0" for no detection of a corresponding spot for
respective pulsed radiation sources being tracked. The output or detect
array may be stored in memory of the camera. Starting at step 1414, zero
run length statistics may be determined in an effort to identify a unique
PRF code of the pulsed radiation source being tracked. At step 1414, the
detection array may be scanned for sequences of no detections, and the
length of each sequence of no detections (e.g., series of `0`s in the
detection array) may be stored in another array, Larray. Each length of
zero detection frames may be saved in memory 1416.

[0065] At step 1418, maximum and minimum zero run length array may be
determined. At step 1420, which may be simultaneously performed with step
1418, a histogram of a first four results of the zero run length array
may be determined and stored in memory 414. A maximum of the histogram of
the zero run length array may be created at step 1422, and a number of
histogram bins of the zero run length array may be determined at step
1424. At step 1426, the maximum of the histogram of the zero run length
array may be determined, and number of histogram bins of the zero run
length array may be determined at step 1426. At step 1428, a feature
vector tree/lookup table may be used to look-up a PRF code 1430 that
matches the zero run length array statistics and further used to
determine the PRF code 1430 of the pulsed radiation source that is being
tracked by the camera.

[0066] Although the process 1400 of FIG. 14 is configured to track a
single pulsed radiation source, it should be understood that the process
1400 may be configured in such a way as to track multiple pulsed
radiation sources simultaneously, as indicated by dashed feedback line
1432. After a last frame is determined to be taken at step 1408, the
process 1400 in step 1410 focuses on pixels within the area that the spot
was detected. However, the process 1400, as provided by feedback line
1432, may continue to repeat steps 1404 and 1406 for each pair of MWIR
images 1402 (i.e., pair of frames of image data) as additional image
frames are collected to perform step 1410. The image frames collected to
perform step 1410 may simultaneously be used to identify and track other
pulsed radiation sources if in the field-of-view of the camera.

[0067] With regard to FIG. 15, a graph 1500 showing illustrative detection
of spots from a pulsed radiation source using an imaging sensor is shown.
The graph 1500 includes three sets of integration windows 1504a, 1504b,
and 1504c (collectively 1504) of an imaging sensor of a camera. During
the integration windows 1504, which are shown as pulses having a frame
rate of approximately 45 Hz and integration time of 6 ms, pixel detectors
that are being illuminated by photons in a field-of-view of optics of the
camera may sense an optical image of a scene and/or spots of a pulsed
radiation source. For the example shown, the PRF of the pulsed radiation
source is approximately 9 Hz. Between each of the sets of integration
windows 1504a, 1504b, and 1504c, a phase delay of one integration time
(e.g., 6 ms) is added. It should be understood that alternative
integration times may be used.

[0068] In operation, and as shown in the graph 1500, there are two missed
spot events 1508a 1508b, which indicates that the pulsed radiation source
pulsed outside of an integration time of the imaging sensor, and are,
therefore, not detected. A detected spot event 1508c occurs within an
integration window 1510a of the imaging sensor, and is, therefore,
detected. From the integration window 1510a and beyond for a certain time
period, integration windows 1510a-1510n are performed on a periodic
basis, as opposed to the sets of integration windows 1504 that have a
more limited wait time and then have a phase delay before a next set
(using the process 1300 of FIG. 13), to determine whether the parameters
of the camera are able to be used to detect, track, and identify the
pulsed radiation source. As shown by spot events 1508d and 1508e, the
spot events fall within integration windows 1510, which means that there
is a high degree of likelihood that the parameters of the camera can be
used to determine the pulsed radiation source. It should be noted that if
the spot events 1508d and 1508e do not occur within the integration
windows 1510, then it is determined that the parameters of the camera are
not aligned with the pulse repetition rate of the pulsed radiation
source, and the process of FIG. 13 would repeat until the correct
parameters are used to identify the PRF code.

[0069] The magnitude of the spot(s) may be a sum of all of the pixels in a
tight spot neighborhood that exceeds a threshold value. In one
embodiment, a Gaussian spot detection mathematical algorithm may be
utilized to determine the spot size. Other spot detection mathematical
algorithms may be utilized, as understood in the art. Resulting digital
data arrays (one for each spot) may include measurements of energy of
either the spot or the background.

[0070] In determining a unique PRF code, measurement parameters may be
generated, as described with regard to FIG. 14. Eight illustrative
features or statistics are identified in TABLE III, and include ZRL
maximum, ZRL count, ZRL minimum, max counts, and histogram values. These
features have been found to be sufficient to allow for unique
identification of all 448 PRF codes. A reduced set of features
(right-hand column of TABLE II) may alternatively be utilized to
determine PRF codes.

[0071] As an example of the pulsed radiation source detection process 1400
described in FIG. 14, TABLE III shows illustrative results for 100-frames
of image data. As understood in the art, pulsed radiation sources are
generally separated by a minimum of 0.01 Hz. In one embodiment, the frame
count starts with a spot detection of a pulsed radiation source. When a
spot of the pulsed radiation source is detected in a frame of image data,
a `1` is recorded, and when a spot of the pulsed radiation source is not
detected in a frame of image data, a `0` is recorded. Once n-frames of
image data are collected and output at step 1410, the rest of the process
begins to determine zero run length statistics.

[0072] TABLE III shows illustrative results of counting the number of
zeros between spot detections. The number of zeros between spot
detections defines a zero run length (ZRL) value for each contiguous
group of zeros (i.e., a run of zeros) in the 100-frames of image data
shown in TABLE II. The count of 0's between 1's (left column of TABLE
III) shows the number of frames of 0's (i.e., no spots detected) between
each of the frames of 1's (i.e., spot detected). For example, because a
spot was detected in frame 1, there are 0 spots between a previous frame
that detected a spot. Thereafter, 9 frames (frames 2-10) of no spot
detections occurred. Between the next frame in which a spot was detected
(i.e., frame 11), 16 frames (i.e., frames 12-27) passed without a spot
being detected, and so on. The right-hand column of TABLE III shows zero
run length counts in order encountered (i.e., the left-hand column
without any 0's). In other words, the ZRL count is 9 between the first
two frames with spots, then 16, 26, 16, 9, and 16.

[0073] The length of ZRLs varies as a function of the pulse repetition
rate of the pulsed radiation source, the frame rate of the imaging
sensor, the frame integration time, and a total number of frames in a
frame data set.

[0074] A feature set may be derived from the contents of the right-hand
column of TABLE III. The features in the feature set separate the 448 PRF
codes of pulsed radiation sources may be defined as:

[0075] (1) The maximum value of ZRL, in this example 26 (i.e., 26 is the
highest number in the right-hand column of TABLE III).

[0076] (2) The minimum value of ZRL, in this example 9.

[0077] (3) The count or histogram bins of the total number of zero runs or
spots detected in different frames of image data, in this example 6
(i.e., the set including 9, 16, 26, 19, 9, 16 is a set size having a
total number of zero runs equal to 6).

[0078] A histogram approach may be used to determine a count of each value
determined by the feature set. Since the number of different values can
vary with each set of input parameters (e.g., frame rate and integration
window of the imaging sensor), the histogram approach provides a
relatively simple way to accumulate a count of the number of identical
values from the ZRL statistics (see TABLE III, right-hand column). An
illustrative truncated histogram is shown in TABLE IV.

[0079] Extracting non-zero values from the histogram of TABLE IV provides
two of the five features of the ZRL statistics (i.e., max of histogram
and # of histogram bins). In addition, the maximum counts feature is also
included in the results shown in TABLE III. The above process for
determining ZRL statistics and feature set may be used for tracking and
identifying PRF codes from one or more pulsed radiation sources
simultaneously.

[0080] With regard to FIG. 16, a timeline showing process 1600 for
simultaneously tracking and identifying PRF codes from one or more pulsed
radiation sources. The process 1600 starts at time T0, where a first
pulsed radiation source is detected at step 1602a. At step 1602b, the
first pulsed radiation source is tracked. In tracking the pulsed
radiation source, a region of pixels local to a spot of the pulsed
radiation source is identified and monitored for additional spots to be
detected. At step 1602c, first pulse radiation source is identified by
its PRF code. In one embodiment, zero run length statistics may be used
to determine a specific PRF code. At step 1602d, an operator or user may
be notified of the first pulsed radiation source identity. By identifying
the PRF code, the user can determine a type of pulsed radiation source
that is being used for targeting purposes. In addition to identifying the
pulsed radiation source, the user may be presented with a specific target
that is being illuminated by the pulsed radiation source. Still yet, the
user may be presented with information associated with the PRF code, such
as weapon type or other related information that uses a pulsed radiation
source with a particular PRF code.

[0081] Continuing with FIG. 16, the process 1600 includes detecting an
nth pulsed radiation source at step 1604a starting at time Tn.
It should be understood that one or more other pulsed radiation sources
may be tracked between detecting the first and nth pulsed radiation
sources. Steps 1604b, 1604c, and 1604d are the same or analogous to steps
1602b, 1604c, and 1604d, but using pixels that are being intermittently
illuminated by the nth pulsed radiation source. As described with
regard to FIG. 14, a Gaussian spot detection mathematical algorithm may
be utilized to identify spots of the pulsed radiation sources.

[0082] FIGS. 17A and 17B are illustrations of an imaging sensor 1700 at
times T=0 and T=n. At time T=0, the imaging sensor is sensing a spot 1702
being generated by a pulsed radiation source. The spot 1702 may occur
periodically or aperiodically depending on a phase difference between the
pulsed radiation source and sensor parameters. As described above, a
track file is initiated when a spot of a pulsed radiation source is
detected by monitoring pixels (e.g., 5×5 pixel matrix) local to
pixel(s) that initially sensed a spot. In one embodiment, coordinates of
the pixels on the imaging sensor 1700 that are sensing the spot of the
pulsed radiation source may be determined and presented to the user. In
another embodiment, rather than using the coordinates of the pixels on
the imaging sensor 1700, geographic coordinates that are being imaged
onto the imaging sensor 1700 may be presented to the user. The geographic
coordinates of a scene may be established using a variety of techniques,
as understood in the art.

[0083] With regard to FIG. 17B, the imaging sensor 1700 may be sensing
spots 1702, 1704, and 1706 of multiple respective pulsed radiation
sources at time T=n. Although shown as spots being sensed at the same
time, it should be understood that the spots 1702, 1704, and 1706 may be
sensed at different times during a time window in which multiple pulsed
radiation sources are illuminating targets within a scene being projected
onto the imaging sensor 1700. During the time window, different frames of
image data captured during integration times of the imaging sensor 1700
may capture the spots at different pixels within the imaging sensor 1700.

[0084] With regard to FIGS. 18A and 18B, an electronic display 1800 that
is part of the camera for a user to view is shown. The electronic display
1800 may display two portions, a scene portion 1802a and information
portion 1802b. The scene portion 1802a shows an optical representation of
a scene that is being imaged onto the imaging sensor, where the scene
includes structures 1804a, 1804b, 1804c, and 1804d (collectively 1804).
Overlaying the scene displayed on the electronic display 1800 is a
graphical spot representation 1806 (Spot A) of the spot 1702 being imaged
onto the imaging sensor 1700 (FIG. 17).

[0085] Within the information portion 1802b of the electronic display 1800
is information 1808 associated with the graphical spot representation
1806. The information 1808a may include coordinate information, such as
azimuth coordinate (az), elevation (el) coordinate, distance, and PRF
code or pulsed radiation source type. In addition to displaying PRF code
or pulsed radiation source type, a weapons system with which the PRF code
or pulsed radiation source type may be identified by searching or
cross-referencing a table that includes weapons systems indexed by PRF
code and/or pulsed radiation source type. An identification of the weapon
type may be displayed with or as an alternative to displaying the PRF
code. The identification may be displayed as a name (e.g., Hellfire
Missile) or graphical representation (e.g., graphic of a helicopter) to
provide the user of the camera with sufficient information to determine
the type of weapons system or vehicle carrying the weapons system with
the pulsed radiation source. TABLE V shows cross-referencing information
for determining a weapons type from a PRF code.

[0086] With regard to FIG. 18B, in the same manner as shown in FIG. 18A,
graphical spot representation 1806 is shown in addition to other
graphical spot representations 1810 and 1812, which is indicative of
three pulsed radiation sources being tracked. As shown, each of the
graphical spot representations 1806, 1810, and 1812 have different
patterns to alert a user that the spots are being sourced by pulsed
radiation sources having different PRF codes. In electronic display
portion 1808b, coordinate information of the spots 1806, 1810, and 1812
may be displayed for the user to view.

[0087] Once the PRF code is identified, the camera may be configured to
provide visual, audible, vibration, or other indication that one or more
pulsed radiation sources are being tracked. If the camera is configured
to recognize an enemy PRF code, then the camera may be configured to
notify the user with one or more possible alerts of an enemy weapons
system being within an area in which the camera can identify the enemy's
PRF code, especially if the power levels are high enough to determine
that the location in which the user is located is being directly
targeted. The alerts or counter-measures may include an audible, visual,
sensory (e.g., vibration), or other alert type to notify the user of the
enemy PRF code.

[0088] The previous detailed description is of a small number of
embodiments for implementing the invention and is not intended to be
limiting in scope. One of skill in this art will immediately envisage the
methods and variations used to implement this invention in other areas
than those described in detail. The following claims set forth a number
of the embodiments of the invention disclosed with greater particularity.